Research and application of integrated fracturing fluid system for unconventional natural gas in coal measures

To solve the problems of poor application flexibility and non-adjustable performance of the current fracturing fluid system in unconventional natural gas of coal measures, an integrated fracturing fluid system is researched. In this study, the experimental evaluation was performed for the viscosity increase, drag reduction, sand suspension, temperature and shear resistance, gel breaking, additive compatibility, anti-swelling and surface tension of the integrated fracturing fluid system based on three kinds of integrated thickeners in combination with the field clay stabilizer, cleanup additive and gel breaker. Meanwhile, the field application effect of integrated fracturing fluid was analyzed. The results show that: the viscosity of the integrated fracturing fluid system is flexible and adjustable, which increases with the increasing of the volume fraction of the integrated thickener. Specifically, the viscosity can be adjusted within the range of 3-200 mPa·s. The high-viscosity liquid has excellent sand suspension performance, and the viscosity of 1.0% volume fraction integrated fracturing fluid is higher than 100 mPa·s at the temperature of 60℃ and the shear rate of 100 S⁻¹. Besides, the integrated fracturing fluid system has good compatibility with various additives, with easy gel breaking, a drag reduction rate>70%, an anti-swelling rate>70% and a surface tension<28 mN/m. Definitely, the integration is mainly realized in the function and application. In terms of function, the slick water, linear glue and cross-linked hydraulic fracturing fluid system are integrated, which can meet the different requirements of various fracturing stimulation technologies of gas reservoir for fracturing, drag reduction, anti-swelling, sand carrying and rapid flowback. As for application, the integrated fracturing fluid system has been successfully applied in the coalbed methane, shale gas and tight sandstone gas wells in the east edge of Ordos Basin. In general, the integrated fracturing fluid promotes the test on unconventional gas fracturing technologies, improves the effect of fracturing stimulation, and shows good adaptability to various gas reservoirs and fracturing stimulation technologies.